Switched-capacitor Units Research Articles

A Multilevel Switched Capacitor Inverter with Reduced Components and Self-Balance

This paper presents a novel 13-level switched capacitor multilevel inverter, which uses less devices to achieve six-fold voltage gain. The proposed topology structure consists of twelve transistors, two diodes, and three capacitors. It is worth mentioning that characteristics as having five complementary switch pairs and self-balanced electric capacity voltages are conducive to simplifying the control strategy. Moreover, the above components constitute the switched capacitor unit and L-type unit. The inverter can acquire more voltage levels and a higher voltage gain by using multiple L-type units with fewer elements. Furthermore, the cost function is employed to comprehensively appraise the performance of the proposed inverter. The comparison with other existing 13-level inverters shows that the proposed multilevel inverter can effectively decrease the value of the cost function. Finally, the simulation and experimental results are presented to demonstrate the feasibility and effectiveness of the 13-level inverter.

Equalization circuit based on switched‐capacitor units and graph networks for series‐connected cell strings

SummaryAn analysis and design method of the equalization circuit based on switched‐capacitor (SC) units and graph networks is proposed in this paper. In the analysis method, the SC equalization circuit is decomposed into multiple SC units and one or more graph networks, which can simplify the analysis process. The effects of circuit parameters and structure on the equalization performance are analyzed in detail. And the average resistance distance among cells is proposed to mathematically analyze and compare the equalization path of the SC equalization circuits. Based on four types of SC units and graph networks of the equalization circuit, a design method of the SC equalization circuit and two SC equalization circuits are proposed. The proposed SC equalization circuit based on cell equalization units has the optimal equalization speed. The proposed SC equalization circuit based on cell equalization units and substring equalization units implements the trade‐off between equalization speed and device number. Simulation and experimental results are provided to verify the validity of the proposed analysis method and SC equalization circuits.

A nine‐level T‐type inverter (9L‐TTI) with voltage boost capability

AbstractThis paper introduces a 9L T‐type boost inverter (9L‐TTI) based multilevel topology, which generates a nine‐level output voltage in the boost mode. This topology uses 12 switching elements alongside less voltage stress and one switched capacitor unit. This is the significant advantage of the mentioned topology. Following the discussion of the advantages of the provided design, a comparative study is conducted. This results in a reduction in device counts, cost‐effectiveness, and voltage stress on the devices. For switching scheme, fundamental switching frequency‐based modulation is incorporated by having nearest level control (NLC) technique. For proper validation of this work, it is also demonstrated through test results. Here the results are demonstrated at different load conditions, which include resistive and inductive loads. Further, it is demonstrated at different modulation indices and total harmonic distortion (THD) of converter voltage and current for RL‐load, is validated from the power quality improvement point.

Three-Phase Boost Multilevel Inverter Based on Coupled-Structure Switched-Capacitor and V2SVM

Recently, a new type of three-phase boost inverters was developed by using switched-capacitor (SC) units to feed the traditional three-phase inverting bridge. With the cooperation of the coupled structure and a specific modulation strategy, this type of inverters has many attractive features. In this article, an SC-based multilevel inverter (MLI) with this coupled structure is developed by using a triple-mode SC unit with varied terminal voltage to feed the three-phase bridge. Compared with the existing topologies, the proposed SCMLI has advantages of higher boost factor and more output levels. In addition, with the improved virtual vector space vector modulation strategy, the capacitor voltage ripple is optimized by selecting the vector’s redundancy states, and the switching stress dv/dt of the end-side inverting bridge is reduced to two third of its blocking voltage. The topology, working principle, capacitors’ voltage ripples, and power losses as well as comparative study are analyzed in detail. Finally, its feasibility and performance are experimentally evaluated by a downscale prototype with a rated power of 1200 W and the measured efficiency is above 97.6%.

A New Generalised Symmetrical/Asymmetrical Boost Integrated Multilevel Inverter with Reduced Components for PV/UPS Applications

ABSTRACT This paper proposes a new generalised boost integrated multilevel inverter (MLI) with reduced components. The proposed MLI is developed by using a modified boost integrated switched capacitor unit, which provides four-level output from each cell. The operation of the proposed MLI for symmetrical 17-level operation with sinusoidal pulse width modulation & nearest level control and asymmetrical 31-level operation with NLC is explained and validated experimentally. The experimental results of static and dynamic load conditions are analysed and discussed in detail. In addition, the proposed topology is compared with recent boost MLI topologies in terms of component count, device stress, efficiency, capacitor size and cost. From the comparative study, it is evident that the proposed MLI provides features such as reduced component count, capacitors size, overall cost and improved voltage gain.

Single-Phase 9L Switched-Capacitor Boost Multilevel Inverter (9L-SC-BMLI) Topology

The boosting factor has become a vital feature for a multilevel inverter to be connected with the low voltage PV system. In this paper, an inverter topology with 9 levels has been introduced. With the use of 10 switches and one switched capacitor unit, the proposed 9L-SC-BMLI has achieved nine different voltage states, and it has twice voltage gain. Without any auxiliary circuits, the voltage of the floating capacitor can maintain self-balanced. The additional feature of the proposed 9L-SC-BMLI has been the lower number of switches, voltage stress of reduced magnitude, and inherent polarity reversal of the output voltage without any H-bridge. The 9L-SC-BMLI has been controlled using the PD-PWM technique, i.e., phase-disposition pulse width modulation technique. In order to show the merits of the 9L-SC-BMLI, a detailed comparative study has been provided in the paper with several similar topologies. A number of simulation results have been provided in the paper with different working environments, and these results have been validated with the real-time results accomplished from a laboratory prototype.

Isolated Resonant Switched Capacitor Converter With Voltage Self-Balancing Ability

This article proposes an isolated resonant switched capacitor converter (I-RSCC) for high-voltage applications. The dc capacitors’ voltages achieve self-balancing with the resonant switched capacitor units (RSCUs). The voltage stress of the switching devices is reduced. The isolated rectifier (IR) is used for galvanic isolation and energy transfer. The number of switching devices is reduced by multiplexing parts switching devices functions, which helps the compact design. In this article, the topology and operation principle of I-RSCC are introduced in detail. Then, the output characteristics of I-RSCC are analyzed, including the voltage balance operation, the energy transmission path, the voltage conversion ratio, and the output power. The design example of I-RSCC is also presented. Finally, a 10-kW prototype is built to verify the feasibility of the proposed I-RSCC topology. The results show that soft switching is realized, and the maximum operation efficiency is 96.5% and above 96% at the rated power.

High-Gain Quasi-Switched Boost Inverter With Single Inductor and Continuous Input Current

The unique advantages of impedance source inverters make them more suitable for new energy fields that need to boost and invert low dc voltages. In order to enhance the boost capability, this work derives a new high-gain quasi-switched boost inverter (HG-qSBI) from the original qSBI topology. Specifically, the voltage gain is improved from 1/(1-2 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> ) to 1/(1-3 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> ) by adding one switched-capacitor unit formed by one capacitor, one transistor, and two diodes, here <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> is the duty ratio for shoot-through states of the inverter. It inherits the advantages of single inductor and continuous input current, and the modulation strategy is exactly the same as the original qSBI. Moreover, all components employed in the HG-qSBI withstand the same voltage stress. All these features are verified by both three-phase simulation and single-phase experimental results.

Boost-type common-ground PV inverter based on quasi-Z-source and switched-capacitor

Common-ground type of transformerless photovoltaic (PV) inverters is an effective means to eliminate common-mode leakage current. Recent years, switched-capacitor (SC) technique with the advantage of voltage boosting has been successfully used in this field. In order to inherit the merits of SC-based common-ground PV inverters, and to further improve the performance in the aspects of inrush charging current, input current quality and boost capability of SCs, a new boost-type common-ground (BCG) inverter is developed by inserting a quasi-Z-source (qZS) unit in an SC-based common-ground inverter. Specifically, an SC unit employed in the BCG inverter is fed by the qZS circuit rather than a voltage source, so that the inrush charging current is effectively limited by inductors of the qZS unit. Meanwhile, the boost capacity is further improved and the input current has been continuous. Both circuit configurations of single-phase and three-phase as well as their operation principle and modulation are analyzed in detail. Especially in the three-phase configuration, only one qZS unit is used to feed three SC units and the input current is almost constant. The feasibility of the proposed BCG inverter is experimentally verified by a downscale three-phase prototype.

A modular switched-capacitor multilevel inverter featuring voltage gain ability

This article presents a modular switched-capacitor multilevel inverter which uses two capacitors and a single dc source to obtain triple voltage gain. It is worth noting that the inherent inversion capacity removes the H-bridge, which can efficaciously diminish the voltage stress of switches, and the maximum voltage stress (MVS) on devices is kept within 2Vdc. Additionally, the proposed topology is able to integrate inductive load, and the capacitor voltage self-balancing can be achieved. Moreover, the modular structure also has an expandable topology which can generate more levels and raise the voltage gain by using multiple switched-capacitor units, meanwhile the voltage stress on power switches can be kept within 2Vdc. Furthermore, comprehensive analysis and comparison with other multilevel inverters have been implemented to certify the superiority of the proposed topology. Finally, the steady-state and dynamic performance of the proposed topology is examined through a seven-level inverter prototype, the validity and practicability of the topology are verified by simulations and experiments.

Single-Phase Boost Switched-Capacitor-Based Multilevel Inverter Topology With Reduced Switching Devices

A multilevel inverter (MLI) with a step-up feature has become significant for connecting a low-voltage PV system with a utility grid. An MLI has been presented in this article with a lower component count. The described structure has achieved nine distinguish voltage levels using 12 switches and a switched capacitor unit having twice voltage boost. A self-balancing of the floating capacitor voltage without any auxiliary circuits and precharging has been obtained. The new topology includes fewer switches, reduced voltage stress, and an inherent reversing polarity without the back-end H-bridge, which has been the additional feature of the proposed circuitry. The topology proposed has been controlled with the nearest level control pulsewidth control technique (NLC-PWM). A comprehensive comparative analysis with several similar topologies has been presented in this article to show the merits of the recommended topology. A number of simulation results using PLECS software have been discussed along with experimental results that have been obtained from a laboratory prototype. The validation of the proposed topology has been carried out using different steady-steady and transient operating conditions.

Self-Balanced Multilevel Inverter With Hybrid Double- and Half-Mode Switched Capacitor

Two 17-level inverters based on switched capacitor (SC) are presented in this article. Each of them involves two SC units and a neutral-point-piloted unit. A total of four pairs of transistors, a bidirectional switch, two pairs of diodes, and three pairs of capacitors are employed. All of the switching components are controlled by six pulsewidth modulation signals and all capacitors’ voltages are self-balanced. With an improved selective harmonic eliminated modulation strategy, low-order harmonics are effectively suppressed and switches operate in low switching frequency. In addition to the use of fewer components, high-quality output voltage shape is benefited from the unique topology and reduced capacitor voltage ripple accumulation. Experiment results demonstrate the excellent performance of the proposed inverter. High efficiency is also achieved and the maximum value is up to 98.05%.

A switched-capacitor and floating-capacitor (SCFC) based multilevel boost inverter with a single DC power supply and sensor-less voltage balancing method

This paper introduces a nine-level (9L) boost inverter with reduced number of components. The proposed 9L topology comprises a single DC source, eight switches, and two capacitors, namely a switched-capacitor (SC) and a floating capacitor (FC). The topology consists of two converter units: the SC unit and the FC unit. Both units are cascaded to achieve nine voltage levels with a voltage gain of 2. The inherent voltage boosting capability of the proposed topology makes it suitable for low-scale voltage applications like photovoltaics (PV) and electric vehicles (EVs). A sensorless method is introduced to stabilize the requisite voltage across the FC for any undesirable changes in input voltage. The performance reveals that the voltage across the FC does not deviate with changes in the modulation index, power factor of load, pulse width modulation (PWM) methods, or the operating frequency. And, when the input voltage fluctuates, the voltage across the FC is naturally adjusted to the new desired value within 0.6 s. The topology operates over a wide range of modulation indices (0 to 1) and different types of loads. A generalized topology is also developed to get a high output voltage along with a higher number of intermediate voltage levels. A comprehensive analysis is presented to show the effectiveness of the proposed topology over the recent topologies.

A new high‐level boost inverter topology with reduced device count

AbstractThe requirement of a boosting aspect for the power electronic converter is essential for the fuel cell, solar PV, and battery‐based applications as the generated voltage is of low voltage magnitude. In these low‐voltage applications, a new boost inverter topology has been suggested, where the power conversion will happen in a single‐stage instead of two‐stage (dc–dc converter + two‐level inverter). The proposed topology consists of 11 power semiconductor devices, one switched capacitor unit, and two dc voltage sources that are arranged in the magnitude of 1:3. This arrangement is able to achieve an output voltage of 15 levels with a boosting factor of 1.75. The other advantages of the designed topology have been the reduced device count with the self‐balancing of capacitor voltage and improved efficiency with better power loss sharing among the switches. By accumulating additional switched‐capacitor units to the proposed basic structure, the proposed inverter can be extended to support a greater number of levels and a higher voltage gain. A comprehensive assessment has been accomplished with single‐source and dual‐source topologies, and the proposed topology shows the improved design. A low‐power laboratory porotype has been used to endorse the proposed topology with real‐time conditions.

A 15-Level Switched-Capacitor Multilevel Inverter Structure With Self-Balancing Capacitor

In this brief, a new switched capacitor-based structure is presented for a single-phase multilevel inverter. The proposed structure is capable of boosting the input voltage and producing fifteen voltage levels at the output utilizing two separated DC voltage sources along with a switched capacitor unit. The proposed structure also has self-charging capability and can automatically adjust the capacitor voltage without any sensor. A quantitative comparison with similar structures has been performed to confirm the proposed structure. Furthermore, loss and thermal simulations have been performed for the proposed structure. The functionality of the proposed structure is examined by the simulation results. Finally, a laboratory prototype is implemented to verify the effectiveness and accuracy of the proposed structure and its control method.

Seventeen-Level Inverter Based on Switched-Capacitor and Flying-Capacitor-Fed T-type Unit

To use fewer components to construct a multilevel inverter (MLI) with more levels and high quality of the output voltage, a hybrid MLI is developed by combining a double-mode switched-capacitor (SC) unit with a T-type unit fed by flying capacitors (FCs). The SC unit is used to boost the amplitude of the output voltage to twice the dc input voltage, while the T-type unit is responsible for increasing the number of output levels. A total of ten transistors, four capacitors, and two diodes are used to generate 17 different levels. As two of the four capacitors are charged by a single dc source directly and the other two operate as FCs, there is no capacitor voltage ripple accumulation (CVRA) problem, resulting in high-quality output voltage. In addition to topology, a voltage balance controller of the FCs is developed to cooperate with the APOD-PWM strategy. Compared with other single-phase SC-based MLIs, the proposed inverter has a lower cost per level. Finally, to verify the feasibility of the proposed inverter, both the simulation model and experimental prototype are established. The results show that the proposed inverter has high-quality output voltage waveform and good dynamic response. The measured efficiency is above 96.5 for a wide range of loads, and the maximum value is up to 98.36.

Simulation and Analysis of Three Phase 7-level Hybrid Switched Capacitor Unit Based Multi-level Inverter

Simulation and Analysis of Three Phase 7-level Hybrid Switched Capacitor Unit Based Multi-level Inverter

Compare the Symmetric Hybridized Cascaded MLI with 17 levels with the Asymmetric Switched Capacitor MLI Topologies for Dynamic Loading

This article builds a symmetric hybridized cascaded a switching capacitor unit in a multilayer inverter and compares it to For 17 level inverters, A switched capacitor unit is utilized with an asymmetric multilevel inverter. In the symmetric hybridized multilevel inverter design, a In the midst of a dual-input dc source, there is a bi-directional switch is utilized to create a modified H-bridge inverter with a five-level output voltage instead of three. In the proposed scenario, In an asymmetric multilevel inverter, the switched capacitor unit substitutes the dc sources. which enlarges By a factor of two, The output voltage has been increased. and the voltage levels at the loads are increased by a factor of two. MATLAB-SIMULINK was used to verify the suggested topology using the staircase modulation approach. The findings show that multilayer inverter topologies with low total harmonic distortion, fewer switches, With greater levels of output voltage are better stable during load disturbance circumstances, making them ideal for renewable energy applications.

Aswitched‐capacitorbased multilevel inverter with reduced circuit components and voltage boosting capability

In this paper a novel topology of switched capacitor based multilevel inverters is proposed. In this topology, to increase the output voltage levels and to add the voltage boosting capability, several switched capacitor units are cascaded in series. Having voltage boosting capability and generating maximum number of output voltage levels using minimum number of circuit components, is a merit for this topology. To highlight the attributes of the proposed topology, it is compared with other recently proposed multilevel inverters on number of circuit components such as power electronic switches, diodes and capacitors, voltage boosting capability, total standing voltage, cost and efficiency. The comparison results verify the superiority of the proposed topology over other proposed topologies on number of circuit components, and number of output voltage levels. It is also clear that, this topology has lower voltage stress on power electronic switches, which makes it an appropriate solution for industrial applications. Finally, to show the capabilities of the proposed topology, and to verify the accurate operation of the topology, circuit analysis as well as the experimental results are provided.

Self-balanced switched-capacitor multilevel inverter with asymmetric double-wing structure

In order to solve the problems of complex structure, high power losses and voltage stress of switches of existing 13-level inverters, this paper presents a new multilevel inverter (MLI) to convert a single DC source’s voltage to an AC voltage with 13 levels. It consists of a switched-capacitor (SC) unit, a T-type unit and an inverting half-bridge. The SC unit can be placed either on the right side of the DC source to halve the input voltage and supply it to the end-side T-type unit, or on the left side of the DC source to double the input voltage and supply it to the end-side inverting half-bridge. Of course, multiple SC units with the same circuit configuration can be placed on both right and left sides of the DC source, simultaneously, to generate more output levels. In addition to flexible structure, the proposed MLI has the advantages of low standing voltage of switches, high boosting capability and power conversion efficiency as well as self-balanced capacitor voltages, which is very suitable for renewable energy sources applications such as photovoltaic and fuel cells. The circuit configuration, working principle, performance analysis under the nearest level modulation and comparative study are presented in detail. And experimental results are provided to evaluate steady state and dynamic characteristics of the proposed MLI.